The present invention relates to an image forming apparatus.
An image forming apparatus is a device in which an electric charge is applied to an image carrier, such as a photoconductor, and a latent image is formed by removing this electric charge from selected areas of the photoconductor surface using an exposure apparatus, such as a laser or a light emitting diode. Further, in this device, a visible image is obtained by causing a toner to attach to the charged positions in this latent image using a development apparatus. Such an apparatus is an electrophotographic printing type image forming apparatus, which has come into common use in recent years.
This electrophotographic printing type image forming apparatus uses an endless belt, that is driven in circulation, as an image carrier.
This endless belt provides a higher degree of freedom with respect to the layout of the exposure apparatus, development apparatus and other apparatuses that are mounted therewith, and the use of such an endless belt makes it possible to downsize the image forming apparatus.
The endless belt is supported by multiple rollers. Such rollers generally comprises a drive roller for applying a drive force to the belt, a tension roller for adding tension to ensure stable belt feed, and multiple idle rollers for defining the belt feed path.
The above-stated rollers have a predetermined inherent eccentricity in conformity to the machining accuracy thereof. Such eccentricity causes fluctuation of the belt feed speed and misregistration in the image formation, and, hence, image distortion occurs, resulting in a considerable deterioration of the image quality. Furthermore, in a color image forming apparatus for forming a multicolor image through overlay of multiple monochromatic toner images, a misregistration in color overlay can be caused by roller eccentricity, resulting in a considerable deterioration of the image quality.
The above-stated problems are not limited to the image carrier. The same problems are found in an intermediate transfer member such as used in a so-called intermediate transfer member type image forming apparatus, wherein an image is formed on a recording medium after a toner image that has been formed on the image carrier has been transferred onto a belt-shaped intermediate transfer member.
The misregistration of an image caused by roller eccentricity can be reduced by keeping the eccentricity within a predetermined range through a high precision machining of a roller. However, improved machining accuracy involves higher machining cost. For this reason, application of this principle has been limited.
To solve this problem, various proposals have been made involving techniques for meeting the required image level without depending on high roller machining accuracy. For example, Japanese Application Patent Laid-Open Publication No. Hei 08-137153 discloses a method wherein a value obtained by subtracting a predetermined value from the distance between the exposure point and the transfer point is defined as an integral multiple of the peripheral length of a drive roller, whereby the influence of image misregistration on the belt-shaped image carrier, resulting from roller eccentricity, is cancelled on the transfer member.
However, the above-stated technique has been intended to solve the problem of deterioration in image quality caused by the eccentricity of a drive roller. No action has been taken for dealing with the eccentricity of idle rollers that are commonly provided in multiple numbers. Accordingly, when the above-stated technique is adopted, it is necessary to machine all idle rollers to an accuracy sufficient to ensure that a predetermined level of eccentricity is not exceeded. However, this directly results in higher production costs.
The object of the present invention is to provide an image forming apparatus that is free from image misregistration and can be economically produced.
The foregoing object of the present invention can be achieved by an image forming apparatus comprising a belt-shaped carrier that is supported on a drive roller, multiple idler rollers and a tension roller; a latent image forming apparatus mounted on the belt-shaped carrier; a developing apparatus for applying toner on a latent image formed by the latent image forming apparatus; and a transfer apparatus for transferring the toner image formed by the developing apparatus.
The above-described image forming apparatus is further characterized in that, when a path leading from the drive roller to the tension roller in the forward direction of movement of the belt-shaped carrier is defined as a drive roller downstream path, and a path leading from the tension roller to the drive roller is defined as a drive roller upstream path, the amount of eccentricity of any idle roller located on the drive roller downstream path is made smaller than that of any idle roller located on the drive roller upstream path, where the latent image forming apparatus is arranged on the drive roller downstream path.
The foregoing object of the present invention can also be achieved by an image forming apparatus, as described above, which is characterized in that, when a path leading from the drive roller to the tension roller in the forward direction of movement of the belt-shaped carrier is defined as a drive roller downstream path, and a path leading from the tension roller to the drive roller is defined as a drive roller upstream path, the amount of eccentricity of any idle roller located on the drive roller upstream path is made smaller than that of any idle roller located on the drive roller downstream path, where the latent image forming apparatus is arranged on the drive roller upstream path.
The foregoing object of the present invention can also be achieved by an image forming apparatus, as described above, that is characterized in that, when the radius of the idle roller is xe2x80x9crxe2x80x9d, the eccentricity thereof is xe2x80x9cexe2x80x9d, the winding angle thereof xcex8[rad] and the maximum permissible misregistration is xe2x80x9cdxe2x80x9d, the eccentricity xe2x80x9cexe2x80x9d of the idle roller, that is arranged on the path that includes the position on which the latent image forming apparatus, is located, is expressed as e less than d(xcex8/xcfx80).
The foregoing object of the present invention can also be achieved by an image forming apparatus, as described above, that is characterized in that the eccentricity of the idle roller having a greater winding angle of the belt-shaped carrier is smaller than that of the idle roller having a smaller winding angle.
The foregoing object of the present invention can also be achieved by an image forming apparatus comprising a belt-shaped intermediate transfer member that is supported on a drive roller, multiple idler rollers and a tension roller, multiple monochromatic image forming means mounted on the belt-shaped intermediate transfer member; a first transfer apparatus for transferring, to the belt-shaped intermediate transfer member, a plurality of monochromatic toner images formed by the multiple monochromatic image forming means; and a second transfer apparatus for transferring, to a recording medium, a colored image obtained by overlaying the plurality of monochromatic toner images.
The above-described image forming apparatus is further characterized in that, when a path leading from the drive roller to the tension roller in the forward direction of movement of the belt-shaped carrier is defined as a drive roller downstream path, and a path leading from the tension roller to the drive roller is defined as a drive roller upstream path, the amount of eccentricity of any idle roller located on the drive roller downstream path is made smaller than that of any idle roller located on the drive roller upstream path, where the latent image forming apparatus is arranged on the drive roller downstream path.
The foregoing object of the present invention can also be achieved by an image forming apparatus, as described above, which is characterized in that, when a path leading from the drive roller to the tension roller in the forward direction of movement of the belt-shaped carrier is defined as a drive roller downstream path, and a path leading from the tension roller to the drive roller is defined as a drive roller upstream path, the amount of eccentricity of any idle roller located on the drive roller upstream path is made smaller than that of the idle roller located on the drive roller downstream path, where the latent image forming apparatus is arranged on the drive roller upstream path.
The foregoing object of the present invention can also be achieved by an image forming apparatus, as described above, that is characterized in that, when the radius of the idle roller is xe2x80x9crxe2x80x9d, the eccentricity thereof is xe2x80x9cexe2x80x9d, the winding angle thereof is xcex8[rad] and the maximum permissible misregistration is xe2x80x9cdxe2x80x9d, the eccentricity xe2x80x9cexe2x80x9d of the idle roller, that is arranged on the path that includes the position on which the transfer point is located, is expressed as e less than d(xcex8/xcfx80).
The foregoing object can also be achieved by an image forming apparatus characterized in that the eccentricity of the idle roller having a greater winding angle of the belt-shaped intermediate transfer member is smaller than that of the idle roller having a smaller winding angle.
The foregoing object of the present invention of the present invention can also be achieved by an image forming apparatus as described above, wherein a support member is provided for supporting the tension roller rotating shaft in a linearly movable manner, and the support member comprises an elastic member.
The above-described image forming apparatus is further characterized in that, when the peripheral length of the belt-shaped carrier or intermediate transfer member is xe2x80x9c1xe2x80x9d, the width is xe2x80x9cwxe2x80x9d, the thickness is xe2x80x9ctxe2x80x9d, Young""s modulus is xe2x80x9cExe2x80x9d, the total of the eccentricities of all rollers which support the belt-shaped carrier or intermediate transfer member is xe2x80x9cxcexa3exe2x80x9d, the maximum permissible image position misregistration is xe2x80x9cdxe2x80x9d and the angles formed by the tension roller traveling direction and the upstream and downstream paths of the belt-shaped carrier or intermediate transfer member is xcex1 and xcex2, then the spring constant k of the elastic member can be expressed as k less than wtE(cos xcex1+cos xcex2)d/(1xcexa3e).